The number of vehicle collisions with animals on the nation's roadways is growing, creating serious safety, wildlife management and endangered species protection issues that are forcing state and local governments to spend millions of dollars to keep the animals off the roads.

The collisions highlight the mounting problem of roadways and housing developments encroaching on wildlife habitat. Roads -- from federal highways to off-road trails -- are estimated to interfere with the ecology of nearly a quarter of all land nationwide, making it difficult for everything from black bears to tiger salamanders to migrate each year to winter feeding and breeding grounds.

The issue has become especially important in protecting threatened species. For example, in the Mojave Desert in Southern California, hundreds of endangered desert tortoises have been crushed by off-highway vehicles while crossing trails on Bureau of Land Management property. BLM closed the trails eight years ago to protect the tortoises, but recently opened them back up. Now, environmentalists fear the opening of the trails will accelerate the trend of tortoise population declines in the region.

While some say the federal government has been slow to respond to the dilemma, states such as Texas and Colorado have spent or are planning to spend tens of millions of dollars to construct underpasses and erect fences to guide wildlife beneath highways in areas where animal-vehicle collisions have been a particular concern.

In Colorado, highway officials are using signs that are triggered by animal-detection sensors and warn motorists of an approaching animal. They are also using roadside reflectors that deflect headlights in a way that scare away deer. On one stretch of U.S. 36 north of Boulder, Colo., the reflectors have cut vehicle-animal crashes by an estimated 60 percent.

The human cost

Animal-vehicle collisions killed more than 200 people in the United States last year, according to federal records, and injured as many as 6,000 more, said Michael Conover, a wildlife biologist at Utah State University's Berryman Institute, which studies human-animal conflicts.

"It's a significant and costly problem," said Keith Knapp, a civil engineer at the University of Minnesota who directs the Deer-Vehicle Crash Information and Research Center, a government-funded coalition that sponsors crash-mitigation projects in eight states from Texas to Connecticut.

Most of the collisions involve deer, Conover said, noting that the growing number of people living in once-rural areas has contributed to the increase in vehicle-animal collisions.

"Urban sprawl means suburbia and deer habitat intersect in many parts of the country," said Kim Hazelbaker, senior vice president of the Highway Loss Data Institute, an automobile insurance funded research group. "If you're driving in areas where deer are prevalent, the caution flag is out."

This bison in Yellowstone National Park is licking salt on the roads left from passing vehicles, creating a potential danger. Courtesy of NPS.

And no time is more dangerous than November and December, when thousands of deer and other wild animals are crossing the estimated 4 million miles of roads and highways nationwide in search of mates and winter feeding grounds, experts say.

States with large deer populations are the worst, and Texas leads the way. A total of 227 people died in vehicle-animal collisions in the Lone Star State between 1993-2007, according to the Highway Loss Data Institute.

But the number of vehicle-animal collisions is growing. State Farm, the nation's largest automobile insurer, has reported that animal strike claims have increased 15 percent in the past five years. The company estimates that there were more than 1.2 million claims for damage in crashes with animals during the last half of 2007 and the first half of 2008.

While fatal accidents involving wildlife make up less than 1 percent of the more than 40,000 traffic deaths on U.S. roadways each year, it costs nearly $1 billion to repair the damaged vehicles, Conover said.

"It's a bad economic problem in that you're wasting almost $1 billion to repair the vehicles," he said. "It's a bad situation."

Successful efforts in Wyo.

Because of the risks, states are working to reduce collisions. Wyoming stands out among them, not only for the steps it has taken to address the problem, but also for the many challenges it faces in doing so.

The state has more than 7,000 miles of national highways stretching past mountain ranges and through winding valleys along some of the most rural landscape in the country. In Wyoming, the populations of antelope and deer outnumber the human residents. And because the state is so rural, people drive on average 18,000 miles a year -- by far the most of any state.

"It's just a fact that you're eventually going to end up in a situation on a Wyoming highway where there is going to be wildlife present, either on the side of the road or on the highway itself," said Cody Beers, the wildlife public involvement specialist for the Wyoming Department of Transportation.

In addition, state officials estimate vehicle-animal collisions killed 2,170 pronghorn, deer, elk and moose last year. But those numbers reflect only animals that state workers removed from road rights of way, noted Erin Smith, a spokeswoman for the Wyoming Game and Fish Department. "There are definitely more, and probably significantly more than are reported," she said.

The Game and Fish Department and the state Department of Transportation have taken the labor-intensive step of identifying vehicle-animal collision hotspots across the state. In some of these hotspots the state has spent nearly $4 million on highway underpasses and fencing to guide the migrating animals under roadways.

One major success story that state officials point to is U.S. Highway 30, in Nugget Canyon on the state's southwest side. Annually, it was common for hundreds of animals to be killed there in vehicle crashes. The state highway and game and fish departments put up miles of fencing along the worst stretches of the highway and built six underpasses to allow mule deer, elk and other wildlife to pass through to winter breeding grounds.

"Wildlife vehicle crashes along this route have dropped dramatically," said Beers.

There is only one drawback: The underpasses cost about $500,000 each.

"That's a lot of money," Beers noted.

Trouble in N.M.

In New Mexico, a 5-mile section of U.S. Interstate 40 in pristine Tijeras Canyon east of Albuquerque was plagued with so many vehicle-animal collisions that a group of residents formed a coalition to lobby the state for help.

At the request of the 120-member Tijeras Canyon Safe Passage Coalition, the state Department of Transportation in 2006 paid to study the area, which was troublesome because of its proximity to Tijeras Creek -- a magnet for mule deer, black bears and other thirsty animals.

As part of an already planned highway widening project, the state and volunteers cleared brush and other debris out from three existing underpasses and installed fencing to funnel wildlife under the road. The state also installed motion-sensitive cameras near the highway that trigger flashing signs warning motorists that an animal is about to cross.

Before the measures were completed in September 2007, as many as 30 animals were hit and killed on this section of the highway each year. Since then, two black bears and one mule deer have been hit, said Mark Watson, a wildlife biologist with the state Department of Game and Fish's conservation services division in Santa Fe.

"I think these steps have had a very strong, positive impact," Watson said.

The cleared underpasses and fencing, which cost a total of $750,000, are the first formal wildlife underpasses in the state, but they should not be the last, said Kurt Menke, an Albuquerque geographer who co-chairs the Tijeras Canyon Safe Passage Coalition.

Menke and the group are lobbying state lawmakers to fund a statewide study of vehicle-animal collision hotspots -- an effort he said is aided by a vote by the Western Governors' Association this past summer to make wildlife corridors a priority.

"When you look at roadkill data maps it's quite amazing to see the cluster of collisions at Tijeras Canyon," Menke said. "But there are data gaps across the state where vehicle-animal collisions are a problem. We need to know where the wildlife corridors are located."

Global warming adds to problem

The situation will only get worse in the coming decades, experts say, because more and more animals will migrate north as the climate warms.

Thanks to this modified culvert in Sussex County, N.J., bog turtles and other small animals can now safely access the two wetlands on opposite sides of the road. Photo courtesy of the Department of Transportation.

The International Panel on Climate Change estimates average temperatures in the United States could warm 7 degrees Fahrenheit by the end of the century. Scientists have calculated that for every increase of 1.8 degrees, the vegetation belt shifts 60 miles north or 550 feet higher.

As the vegetation moves, so will thousands of species of mammals, birds, reptiles and amphibians. And because so much of the landscape is crisscrossed with highways, a growing number of wildlife experts argue the nation needs to create wildlife corridors.

The conservation group Wildlands Project has spent more than a decade developing what it calls "wildlife network designs" -- carefully plotted corridors connecting already preserved lands to one another. The group is working closely with BLM, the Forest Service and the National Park Service, as well as private landowners willing to voluntarily set aside a portion of their property as a migration route, said Kim Vacariu, the group's Western director in Portal, Ariz.

Vacariu said the conservation group's ultimate goal is to create a 5,000-mile-long wildlife corridor from Mexico to Alaska. "It's a project that will take generations to complete," he said. "But you've got to start somewhere, and we're creating the building blocks for a connected landscape."

Effects on amphibians

In terms of sheer numbers, amphibians are the biggest victims of road-kill, and simply building highway underpasses and erecting fences will not help them.

A study led by Purdue University estimated that a major reason for the decline in the number of frogs, salamanders and other amphibians in the United States -- and perhaps worldwide -- might be that so many are being crushed on the nation's roadways.

Studying an 11-mile stretch of roads in West Lafayette, Indiana, for 17 months, researchers discovered 65 different animal species among the 10,500 dead animals -- all but a small percentage of which were frogs and other amphibians.

Among the roadkill were 74 dead northern leopard frogs, which Indiana has designated as a species of special conservation concern, and 142 environmentally sensitive eastern tiger salamanders, said Andrew DeWoody, a Purdue biologist who led the study published in April.

DeWoody is helping lead another soon-to-be-published study that will recommend, among other things, installing pipe culverts to allow amphibians to cross under roadways.

"Ultimately it will be up to society to determine how much we want to spend and what species we want to save," he said.

Scott Streater is a freelance journalist based in Colorado Springs, Colo.